While it is known that pupil size varies in its diameter in darkness between individuals from 3 mm to 9 mm, little attention has been paid to the effect of this difference on the night vision and vision in dim light (scotopic vision is dark adapted vision). Those with large pupils suffer from much more light scatter, glare, halo, and related aberrant focus of light rays that can make function under certain conditions of lighting very difficult.
Laser vision correction in particular has added new quality of vision difficulties for many of these individuals. Exposing the retina to light focusing from as much as nine times more surface area essentially magnifies every variation in curvature from the ideal. Currently, only direct acting miotic agents such as pilocarpine are used in an effort to decrease pupil size.
Pilocarpine causes brow ache, ciliary muscle contraction and pseudo myopia, excessive dimness when first applied, and redness. Its effect lasts only a few hours, and it has known, though remote, risk of retinal detachment probably related to pull on the retina from stimulated ciliary muscle contraction. For these reasons it is rarely tolerated or considered a clinically useful alternative for patients with large pupils in dim light.
Another medication used to affect pupil-size is dapiprazole, an alpha-1 adrenergic receptor blocking agent. Dapiprazole is 5,6,7,8-tetrahydro-3-[2-(4-o,tolyl-1-piperazinyl)ethyl]-8-triazolo[4,3-a]pyridine hydrochloride. It is available in a 0.5% solution to partially counteract, or reverse, the dilation effect of phenylephrine, an adrenergic dilating agent, and the dilating and accommodation loss caused by tropicamide. In addition to producing redness upon instillation, dapiprazole has very little effect on pupil size in dim light in clinical application when used topically for this purpose, and therefore its sole use is as a treatment of iatrogenically induced mydriasis produced by adrenergic or parasympatholytic agents.